In bowl, beat butter with icing sugar until fluffy; stir in poppy seeds and lemon rind.
Gradually blend in flour.
Gather dough into ball; chill for 30 minutes if sticky.
On lightly floured surface, roll out dough to 1/4 inch (5 mm) thickness; cut into 2 inch (5 cm) rounds and place on ungreased baking sheets. (Or, press dough into 9 inch/2.5 L square cake pan; prick surface all over with fork.)
Sprinkle with granulated sugar.
Bake in 300Â°F (150Â°C) oven for 20 to 25 minutes for cookies, or 35 minutes for square, or until set and very faintly browned.
Let cookies cool on rack, or let large square cool in cake pan before cutting into bars. (Shortbread can be stored in airtight containers for up to 5 days or frozen for up to 1 month.)